1. Field of the Invention
The present invention relates to an image forming apparatus which includes a developing device including two electrode members, and further includes a detection mechanism for detecting a capacitance between the two electrode members.
2. Description of the Related Art
An image forming apparatus such as an electrophotographic apparatus conventionally includes a developing device which contains toner, which is a developer. Some developing devices are shipped as preinstalled in the main body of an image forming apparatus. Others are packed and shipped by themselves, and a user mounts such developing devices on an image forming apparatus.
As image forming apparatuses have recently been reduced in size, developing devices have also been becoming smaller. Such small-sized image forming apparatuses and small-sized developing devices have become more likely, because of the smallness, to be transported in various orientations under excessive vibrations and stored in various orientations for long periods of time. The toner in even a new developing device is therefore not necessarily evenly distributed in the longitudinal direction of the developing device.
For example, using a developing device in which toner is unevenly distributed to one side in the longitudinal direction can cause image defects such as a white spot (image missing due to an insufficient density). In addition, a drive torque for rotating a developing roller (toner bearing member) and a stirring member of the developing device can become so high that a drive gear may break down. Japanese Patent Application Laid-Open No. 2001-290356 discusses a method for detecting the state of toner in the longitudinal direction of a developing device by arranging three or more electrodes inside the developing device.
According to the detection method discussed in Japanese Patent Application Laid-Open No. 2001-290356, a plurality of electrodes needs to be arranged in the toner container in addition to the toner bearing member. This increases the number of parts and complicates the configuration of the developing device.